If an Indian submarine gets "disabled'' deep underwater, the sailors are sunk since the country has only rudimentary submarine rescue facilities.

Now, in a unique and complex endeavour, Indian and US Navies have come together to practice the rescue of "trapped'' submariners from deep under the sea.

The Indo-US submarine rescue exercise 'INDIAEX-2012' will kick off this week with the US Navy's Undersea Rescue Command flying down a submarine rescue system - a deep-submergence rescue vessel (DSRV) or a submarine rescue chamber (SRC).

The DSRV or SRC will then be shipped to the exercise area off Mumbai, where it will dive deep underwater to "mate'' with "disabled'' submarines to rescue sailors in intricate manoeuvres rarely practiced by Indian sailors.

A DSRV or "mini submarine'', equipped with pressurised chambers, sonars and cameras, can rescue 24 sailors at a time from a depth up to 610 metres after "mating'' with a stricken vessel's hatch.

At present, Indian sailors bank upon "submarine escape pressurized suits'', or the help of diving support ships like INS Nireekshak, but they can be used only for relatively shallow depths.

Navy's endeavour to procure two DSRVs of its own, for about Rs 1,000 crore, has been stuck for well over a decade.

As an "interim measure'' in 1997, India had inked a contract with US Navy for its "global submarine rescue fly-away kit'' service, paying an initial $734,443 for it.

But the agreement got derailed due to the post-Pokhran-II sanctions in 1998. It was later revived in 2004 but there has been a huge delay in setting up the requisite infrastructure needed for it.

This also included fitting of 'Padeyes' - holding devices welded into submarine escape hatches to secure the DSRV - on Indian submarines.

The US rescue system, as per the agreement, will be transported to India within 72 hours of an emergency.